Recovery of sulphur dioxide from gases



NHTED STAT-ES PATENT OF'FIQE RECOVERY OF SULPHUR DIOXIDE FROM GASES Raymond F. Bacon, Bronxville, and Rocco Fanelli, New Rochelle, N. Y.; said Fanelli assignor to said Bacon No Drawing. Application December 24, 1935, Serial No. 55,987

3 Claims. (01. 23-478) This invention relates to the recovery of sulbeing driven off. This is explained, to some ex phur dioxide and has for an object the provision tent at least, by the fact that ammonium sulphite of an improved process for recovering sulphur is a salt of a weak base and a weak acid, and, in dioxide from gases containing sulphur dioxide water solution, it shows a fair hydrolysis into 5 mixed with other gases. The process of the inammonium hydroxide and ammonium bisulphite 5 vention may be employed for the recovery of according to the following equation: sulphur dioxide from gas mixtures containing a T sulphur dioxide in any degree of concentration, (NED203+H2OPl IH4Oh+NHtHSO3 and it is particularly suitable for the treatment The ammohlum hyth'exlde t ls unstable of gas mixtures containing relatively small conand breaks down Into h gas and Water at 10 centrations of sulphur dioxide, such, for example, room fq f t higher temperatures, de-

composition is extensive. It has been proposed as gas mixtures resulting from the roasting of pyrites, ores, concentrates and other metallurgical employ a'mmohlhm hlsutphlte 1h cohJu-hctloh with the ammomum sulphite to retard or preraw materials and products containing metal sulphides vent hydrolysis. 15

The process of the invention may be employed We have found that any aeld strohger than to produce a substantially pure sulphur dioxide water e Weaker thah-sulphhrous field a he product, in either gaseous or liquid form, or to used 1n place f the mmomum bisulphite t0 produce gaseous products containing Sulphur reduce hydrolysis of the ammonium sulphite.

0 oxide in any suitable proportions. The inven- We h that a System as amtion provides an effective and economical method memurh f 'h acid far W to the for producing sulphur dioxide-bearing reagents emmehlum sulphltethlsulphlte mlxtures as for various chemical and metallurgical uses as, sorbents for dilute sulphur dioxide. Not only do for example, in e production of sulphuric a id, 88 solutions show better absorption of sulphur in the production of sulphite cooking liquors, in dioxide but also 5 o dation to Sulphate be- 25 the production of elemental sulphur by r d cause of the smaller concentration of S03 and tion of the Sulphur dioxide, in f i ti and HSOs ions in the original solution. We have also in the leaching of ores. The invention further fohhd that these Solutlehs t ammehmm tprovides an effective and economical method of t w and after ahsorptloh 0t t t reducing or eliminating the injurious effects ree glve up the abserhed Sulphur thexlde more 30 sulting from discharging roaster and other eeshy when the Soluttohs are heatedsmelter gases into the atmosphere, and, at the Any Suitable acid Stronger than water and same time, permits the recovery in useful form Weaker than Sulphurous eeld may be employed of an important component of such injurious in carrying out the process of the invention. gasea Preferably, the acid employed is one which is The process of the invention is of the type in readily soluble in water and stable and substan- Which gases containing sulphur dioxide are tially non-volatile at the temperatures employed treated with a liquid solvent or absorbent, and 1h hbemtmgthe absrbed.su1phur dloxlde' the absorbed sulphur dioxide is expelled by heat- :I'he tohowmg example Illustrates .refsults 40 mg or by reduction of pressure with or Without tamed 1n the treatment of gases containing about heating, the regenerated solvent or absorbent be- 6% of sulphur dloxlde wlth ammomum Sulphlte ing used for the treatment of additional quansolutions containing lactic acid' tities of gases.

It has been proposed heretofore to employ am o; Percentsoz concentrated aqueous solutions of soluble suls f fggg fgg ig f 21533:; if? diiitii ti oi i r 45 phites such as ammonium sulphite to absorb liter met of 10 it t o sulphur dioxide from gases containing the same.

In view of the high solubility of ammonium sulphite at ordinary temperatures, concentrated g? 5 solutions absorb large quantities of sulphur diox- 290 210 12s 32 ide, ammonium bisulphite being formed. The t2; absorbed sulphur dioxide is released by heating 360 300 12s 93 the bisulphite solutions, and a serious difiiculty is encountered when the solutions are heated, In carrying out a process of the invention, the

ammonia or a sublimate of ammonium sulphite sulphur dioxide-bearing gases may be treated 55 with the absorption solution in any manner known to the art of contacting gases and liquids. Thus, for example, the gases may be passed over the surface of a body of solution, with continuous or intermittent agitation of the solution, the gases may be bubbled through a body of the solution, or the gases and the solution may be passed, either co-currently or counter-currently, through a packed tower in contact with one another.

If gases such as roaster gases are being treated, they are preferably cooled and treated for the removal of dust and other objectionable impurities contained therein prior to treatment with the absorption solution.

The absorbed sulphur dioxide may be liberated in any suitable manner. Preferably, the solu tion is heated to a temperature sufficiently high to bring about a rapid evolution of sulphur dioxide, but not high enough to cause substantial vaporization of the weak acid.

Liberation of sulphur dioxide may be carried out at atmospheric pressures or at pressures below atmospheric. When the weak acid employed is volatile at the boiling point of the solution produced in the absorption operation, liberation of the sulphur dioxide should be carried out at a temperature below the boiling point of the solution. Any suitable temperature from the absorption temperature to the boiling temperature of the solution may be employed for liberating the sulphur dioxide. Rapid and effective liberation and recovery of sulphur dioxide may be accomplished by employing a Weak acid which is stable and non-volatile at the boiling temperature of the solution and heating the solution to the boiling temperature.

The apparatus employed in carrying out a process of the invention should be so arranged that available heat may be utilized efi-lciently. Thus, for example, when hot roaster gases are being treated, the heat contained in the gases should be utilized for heating the bisulphite solution from which sulphur dioxide is to be liberated, and the cold bisulphite solution produced in the absorption operation should be utilized for cooling the regenerated absorption solution, after liberation of the sulphur dioxide to avoid wasting the heat contained therein.

The bisulphite solution may be heated in any suitable manner to effect liberation of the absorbed sulphur dioxide. Thus, for example, the solution may be heated in a closed vessel out of contact with other gases, or the solution may be heated by contact with a body or current of another gas to which it is desired to transfer the sulphur dioxide. The gaseous product formed by heating the sulphite solution out of contact with other gases is substantially pure sulphur dioxide and it may be utilized for a suitable industrial purpose directly (diluted or undiluted) or it may be cooled to a suitable temperature and compressed to form liquid sulphur dioxide.

We claim:

1. The process of recovering sulphur dioxide from gases containing the same which comprises treating the gases with an aqueous liquid containing in solution a sulphite and an acid stronger than water and weaker than sulphurous acid to effect absorption of the sulphur dioxide with the production of a bisulphite, and heating the solution to liberate absorbed sulphur dioxide, the acid employed being stable and substantially non-volatile at the temperature of liberation, existing in the solution independently of the action of sulphur dioxide and being employed in an amount not less than that equivalent to about 68 grams of lactic acid per liter and capable of affecting positively the rate of liberation of sulphur dioxide from the absorption solution under the influence of heat.

2. In a process for recovering sulphur dioxide from gases containing the same in which the gases treated with an aqueous solution of ammonium sulphite to effect absorption of the sulphur dioxide with the production of ammonium bisulphite, and the resulting solution is heated to liberate sulphur dioxide, the improvement which comprises incorporating in the solution a water-soluble acid stronger than water and weaker than sulphurous acid to inhibit hydrolysis of the ammonium sulphite and to expedite the liberation of sulphur dioxide under the influence of heat, the acid employed being stable and substantially non-volatile at the temperatures employed in the process, being employed in an amount not less than that equivalent to about 68 grams of lactic acid per liter, and existing in the solution independently of the action of sulphur dioxide.

3. In a process for recovering sulphur dioxide from gases containing the same in which the gases treated with an aqueous solution of ammonium sulphite to effect absorption of the sulphur dioxide with the production of ammonium bisulphite, and the resulting solution is boiled to liberate sulphur dioxide, the improvement which comprises incorporating in the solution a watersoluble acid stronger than Water and Weaker than sulphurous acid to inhibit hydrolysis of the ammonium sulphite and to expedite the liberation of sulphur dioxide under the influence of heat, the acid employed being stable and substantially non-volatile at the temperatures employed in the process, and being employed in an amount not less than that equivalent to about 68 grams of lactic acid per liter.

RAYMOND F. BACON. ROCCO FANELLI. 

